Abstract: A system and method for controlling the endpoint of a product of a pyrolysis reactor is provided. The system can include a pyrolysis reactor, a quench system, a separation section, and a compression and fractionation section. In the system and method, a pyrolysis reactor performs a pyrolysis reaction on a plastic feed to produce an effluent stream, and the effluent stream is transferred to a separation section, wherein it is separated into a heavy liquid byproduct stream and a vapor stream. Portions of the heavy liquid byproduct stream can be recycled to the pyrolysis reactor or used to quench the effluent stream. A portion of the heavy liquid byproduct stream can also be withdrawn from the system as a secondary product. The vapor stream is transferred to a fractionation section, where it is cooled and separated into a light gas stream and a liquid product.